Winter open-water zone remote sensing (2017-2023) and field (2023) data from the Yukon and Kuskokwim rivers and their tributaries in western Alaska

Timing and completeness of freeze-up on northern rivers impacts safe winter travel and may indicate responses to climate change. Open-water zones (OWZs) within ice-covered rivers are hazardous partly because their unpredictability and are suggested to be increasing in extent and persistence due to groundwater upwelling, higher winter discharge, and permafrost degradation. To better understand the distribution, variability, and mechanisms of winter OWZs, we selected nine study reaches totaling 400 kilometers (km) of the Yukon and Kuskokwim rivers and their tributaries for remote sensing analysis and field studies in western Alaska, USA. We identified 51 OWZs from late November optical imagery along these reaches ranging from 60 meters (m) to 9 km in length, inventoried their persistence over six years, and at a subset measured ice thickness, under-ice water depth and velocity, water-column and river-bed physico-chemistry. Concurrently, we investigated if and to what extent sediment was entrained in river ice at these same sites. These locations corresponding to observed OWZs were quantified by size, classified by hydrogeomophic location, and tracked for consistency during the preceding five years in the early (late November) and late (late February or early March) winter periods. A subset of these OWZ were visited in March of 2023 to collect additional field data on snow, ice, and physico-chemistry including ice sediment concentration. This research is part of the Fresh Eyes on Ice and Sediment Ice Learning on the Tanana (SILT) projects.

北部河流封冻的时机与完整程度，会对冬季安全出行造成影响，同时可作为气候变化响应的指示指标。冰覆盖河流中的开阔水域（Open-water zones, OWZs）存在安全隐患，部分原因在于其不可预测性；现有研究表明，受地下水上升、冬季径流量提升以及多年冻土退化的影响，这类水域的范围与持续时长正呈扩大趋势。为深入探究冬季开阔水域的分布特征、动态变化与形成机制，我们选取美国阿拉斯加州西部育空河（Yukon）、库斯科奎姆河（Kuskokwim）及其支流的9处研究河段，总长400千米，开展遥感分析与野外实地研究。我们通过该河段11月下旬的光学影像识别出51处开阔水域，其长度介于60米至9千米不等；我们对这些水域的持续时长开展了为期6年的编目统计，并针对其中部分点位测量了冰厚、冰下水深与流速，以及水柱与河床的物理化学性质。与此同时，我们还针对上述点位探究了河流冰体中是否裹挟沉积物，以及裹挟的具体程度。我们对这些对应已观测到的开阔水域的点位，按规模进行量化分级，依据水文地貌位置进行分类，并追踪了前5年冬季早期（11月下旬）与晚期（2月下旬或3月上旬）的点位一致性变化情况。我们于2023年3月对其中部分开阔水域点位开展了实地考察，采集了积雪、冰体及相关物理化学性质的额外野外数据，其中包含冰体沉积物浓度。本研究隶属于《塔纳纳河冰体与沉积物冰研究新视角》（Fresh Eyes on Ice and Sediment Ice Learning on the Tanana, SILT）项目集群。